ارزیابی تأثیر نیترات پتاسیم و سرمادهی مرطوب بر شکست خواب و خصوصیات جوانه‌زنی و تعیین دماهای کاردینال بذر گیاه سلمکی (Atriplex patula)

Abstract
Atriplex patula is a wild plant from the Chenopodiaceae family that has medicinal, nutritional, fodder and dedesertification applications. In order to determine the type of seed dormancy and characteristics of germination and the method of breaking dormancy and determining the cardinal temperatures of germination in this species, two experiments were conducted separately. In the first experiment, the first factor, potassium nitrate was evaluated at 4 levels and cold stratification as the second factor at 3 levels. The percentage and rate of seed germination were calculated. The second experiment was conducted to determine the germination cardinal temperatures, by 9 temperature levels (0, 5, 10, 15, 20, 25, 30, 35 and 40℃) and by determining the germination rate and fitting the most suitable regression model between temperature and germination rate. In both experiments, each treatment had 4 replications of 25 seeds and the percentage and germination rate were calculated. The results showed that potassium nitrate with a concentration of 250 mg/liter along with cold stratification at 3°C for one week had the most positive effect on the breaking of seed dormancy and the germination percentage and germination rate. the rate and percentage of germination reached 8.16 and 90%, respectively. In the second experiment, the cardinal germination temperatures, including the minimum, optimum and maximum temperatures, were obtained as 1.86°C, 22.5°C and 38.89°C, respectively, and the toothed regression model showed the best fit. According to these findings, seed dormancy in Atriplex patula was determined to be of non-deep physiological type.
Introduction
Wild grassland plants are among the sources that have been considered for new food sources with the rapid increase of the world population and can be used as agricultural plants in the future. Atriplex patula is a herb of the Chenopodiaceae family, which has been reported for its medicinal, nutritional, fodder and dedesertification uses. Atriplex species are halophytes that are distributed in a variety of saline habitats, including the margins of wetlands, coastal areas, hills, and deserts (Bueno et al., 2017). These plants are suitable for dry and semi-arid degraded pastures in terms of compatibility with the environment, being evergreen and growing in poor and salty lands. Domestication of wild plants has obstacles, one of which is the existence of seed dormancy and, as a result, the problem of germination, so in order to improve seed germination, it is necessary to apply treatments to remove the obstacles to germination. According to the type and depth of seed dormancy, various treatments have been proposed to break dormancy and stimulate plant seed germination, which also depends on the genotype of the plant species. In order to determine the type of dormancy and characteristics of germination and a method for breaking dormancy and determining germination cardinal temperatures in this species, two experiments were conducted separately.
Materials and Methods
The first experiment was conducted as a factorial in a completely randomized design with two factors. The first factor was potassium nitrate at 4 levels (0, 250, 500 and 750 mg.L^-1) and the second factor was cold stratification at 3 levels (without cold stratification and cold stratification at +3℃ and +6℃). The number of treatments was 12 and 25 seeds were used in 4 repetitions. The rate and percentage of seed germination were calculated. In order to determine the germination cardinal temperatures, an experiment was conducted in a completely random design by 9 temperature levels (0, 5, 10, 15, 20, 25, 30, 35 and 40℃). Each treatment had 4 replications of 25 seeds. this experiment was done by determining the germination rate and fitting the most suitable regression model between temperature and germination rate.
Results and Disscussion
The results of variance analysis of the effect of treatments used to break seed dormancy in this research, showed that the germination percentage of Atriplex patula seeds and their germination rate were significantly affected by the application of potassium nitrate, and cold stratification, and the interaction of these two treatments with a probability level of 99% (P<0.01). Based on the results, potassium nitrate (250 mg.L^-1) along with cold stratification at 3°C for one week had the most positive effect on seed dormancy breaking and increasing the germination percentage and rate. The rate and percentage germination reached 8.16 and 90% respectively by this treatment. The lowest germination percentage was related to the control treatment (0 mg.L^-1 potassium nitrate × without cold stratification), and the highest germination percentage was 90.00%, related to the interaction of two factors of potassium nitrate 250 mg.liter^-1 × cold stratification at 3℃. Cold stratification treatment had a greater effect on seed dormancybreaking than potassium nitrate treatment. The lack of cold stratification, in different concentrations of potassium nitrate, decreased the germination percentage of seeds, although the treatment of seeds with different concentrations of potassium nitrate had a significant difference with the control treatment, but without the wet cooling treatment, the germination percentage decreased. In the second experiment, the germination cardinal temperature, including the minimum, optimal, and maximum temperatures, were obtained as 1.86, 22.51, and 38.89℃, respectively, and the best model was chosen to be the cardinal temperatures of the tooth-like model. The lowest germination rate (0.4) was observed at 5°C. With the increase in temperature from 5°C to above, the germination rate increased and at 25°C, the highest germination rate was achieved. From the temperature of 25°C and above, the germination rate decreased with a significant difference. Different temperatures with their effect on germination may be useful for evaluating the characteristics of germination and establishment potential of plant species. The issue that should be noted is that the germination rate is more important than the germination percentage in the discussion of plant establishment, because the faster the germination, the more likely the roots will come out of the soil and absorb soil moisture and result better establishment of the seedling (Hashemi et al., 2017).
Conclusion
According to the results of the present research, it was found that seed dormancy in Atriplex patula is of non-deep physiological type. Cold stratification at 3°C is more effective than potassium nitrate in breaking seed dormancy of this plant.